1. Field of the Invention
The present invention relates to the artificial lifting of petroleum from low pressure wells by lifting the petroleum, the sucker rods and chain from one well while utilizing the sucker rods and chain of another well as a counter weight. The present invention has been found to be particularly useful in the offshore petroleum pumping and production art and hence will be discussed with particular reference thereto. However, the present invention is applicable to other types of petroleum pumping and production on land and also subsea. The present invention may also be used to pump saltbrine, sulphur or other minerals contained or suspended in a liquid form.
2. Description of Prior Art
The sucker rod pumping system is the most widely used artificial petroleum lifting system on land today. About 90% of the wells that are in production on land that require the petroleum to be artificially lifted (as opposed to wells with sufficient gas pressure to push the petroleum out of the ground) from say fifteen thousand feet (15,000') or less use sucker rods. Today petroleum organizations are attempting to use sucker rods to go as deep as 18,000 to 20,000 feet.
The device that causes a sucker rod to move up (gravity causes the sucker rod to move down) is called a pump jack in the petroleum industry. A pump jack is a device that is often seen on oil fields with a horse head looking device moving up and down. The horse head is pulling up on the sucker rod and allowing it to fall. As it pulls up on the sucker rod it also pulls up petroleum with the rod and valves connected to the rod. As the horse head moves down the sucker rod drops.
The typical pump jack has several major drawbacks that make it difficult to use on offshore production platforms.
(1) A pump jack takes up a lot of space. In some cases a typical pump jack will take up a deck area of 29 feet by 9 feet. The well heads on a production platform are usually about 7 feet to 8 feet apart, thus not far enough apart to place the pump jacks side by side.
(2) The weight of a pump jack is too great to be supported by most offshore production platforms. When the wells lose their pressure they are often old wells with an old production platform supporting the wells. The production platform in most cases will not have sufficient weight bearing capacity to support a twenty ton pump jack along with the sucker rod pull of about another twenty tons. If the platform has say ten (10) wells, it must be capable of supporting an additional 400 tons of deck load which most likely it cannot.
(3) In wells of twelve thousand feet (12,000) or greater a pump jack will only produce about 50 barrels of fluid a day which most likely is not sufficient production to invest in a new offshore production platform or to rebuild an old production platform.
(4) Most pump jacks require a large rotating counter weight or offset flywheel to help lift the long sucker rods. The counter weight will often set up with the natural frequency of the production platform and destroy the platform.
(5) Each time the sucker rod is dropped by gravity and then instantaneously pulled back up, there is a great stress reversal on the sucker rod. This stress reversal takes place about once every six seconds with a pump jack. The great number of stress reversals will cause the sucker rods to fatigue after a certain time period. The results are that the sucker rod will fail or it must be replaced before it fails.
(6) The fatigue factor of a sucker rod will require that the rod is a greater diameter which will increase the weight of the rod and therefore increase the size of the pump jack and the size of the counter weight of the pump jack. This is one of the major limiting factors that prohibits the use of an 18,000 to 20,000 foot or greater sucker rod. The extra weight of the sucker rod will also increase the cost of the sucker rod and the pump jack.
There are also pumps that are placed at the bottom of the well say at 20,000 feet. These are called submersible pumps. Submersible pumps push the petroleum up the well to the surface. The problem with submersible pumps is that they must work in a very hot and caustic environment; they must push petroleum up against 10,000 to 20,000 feet of hydrostatic pressure and they must work with sand, silt and other debris.
A submersible pump will clog up with the sand, silt or other debris and must be pulled out of the well and be replaced as often as once every two months. Replacing a submersible pump is very costly as expensive labor and equipment must be employed in the pulling and reinstalling of another pump. The well is also shut down for about a week which results in another loss of revenue.
A submersible pump is only used where a sucker rod pump cannot be used or where the production will not be sufficient with a sucker rod pump.
Another type of petroleum pump that is widely used in the petroleum industry is known as the long stroke pump.
There are two types of long stroke pumps although in practice they are both very similar. One type requires a tower that has a sheave at the top. Running over the sheave is a rope or wire rope that has a large counter weight at one end and the other end of the rope is connected to the sucker rod. As the sucker rod is pulled up and out of the well the counter weight at the other end of the rope assists the motor in pulling up on the sucker rod. The other method requires a counter weight well. It still requires a sheave, a wire rope and a counter weight but it also requires a counter weight well. The counter weight well must be bored about 50 feet into the earth. Both systems require a large counter weight.
The problems with both systems are first that they weight a lot due to the large counter weight. They also take up a lot of space due to the counter weight, the counter weight well and or the size of the tower.
Some offshore platforms use the tower type of pump but there are several major limitations. One limitation is the tower itself. The tower adds a wind load to the production platform that is very sensitive to extra wind loading and therefore not more than one or two towers may be added to the platforms; most offshore production platforms have three or more wells. Another limitation is the base size of the tower. They are very large at the base and therefore take up a lot of space. Another limitation is the length of the stroke. The stroke is limited to the height of the tower or the depth of the counter weight well which is about 50 feet. When the height or depth of either unit is over 50 feet the cost of the unit increases at a greater rate.
Two examples of tower type long stroke pumps are EWING, U.S. Pat. Nos. 3,695,117, Oct. 3, 1972, BENDER, 3,248,958 May 3, 1966. Another long stroke pumping unit with a counter weight well is GAULT, 4,062,640 Dec. 13, 1977.
Several other pumping devices have been known and used before and typical examples thereof are shown in U.S. Pat. Nos. 3,640,342 issued on Feb. 8, 1972 to GAULT: 224,862 filed Dec. 18, 1879 to BIGRLOW: 1,970,596 issued Aug. 21, 1934 to COBERLY: 1,928,532 issued Sept. 26, 1933, to GILLESPIE: 3,977,259 issued Aug. 31, 1976 to GOLDFEIN: 4,306,463 issued on Dec. 22, 1981 to KING; 3,018,865 filed June 22, 1956 issued to BLACKBURN: 2,997,887 issued on Aug. 29, 1961 to LOTT: 3,646,833 issued on Mar. 7, 1972 to WATSON. None of the devices however, teach the art of pumping petroleum from two or more wells utilizing one sucker rod inside of one well to act as a counter weight for the second sucker rod inside of a second well thereby increasing pumping efficiency.